Combine the olive oil, onion, garlic, celery, tomatoes, sugar and 1 teaspoon salt in a saucepan. Cook over medium heat, stirring occasionally, until the vegetables are tender, about 25 minutes. Puree until smooth with an immersion blender, or transfer to a regular blender in batches and puree. Season with salt and pepper and keep warm; add water to thin the soup, if desired.

Meanwhile, combine all three cheeses in a bowl. Divide evenly among 4 bread slices and top with the remaining bread. Heat 1 tablespoon butter in a large skillet over medium heat. Cook the sandwiches in batches, adding the remaining 1 to 2 tablespoons butter as needed, until the cheese melts and the bread is golden, 3 to 4 minutes per side. Serve the sandwiches with the soup.

Per serving: Calories 682; Fat 39 g (Saturated 16 g); Cholesterol 66 mg; Sodium 1,373 mg; Carbohydrate 56 g; Fiber 6 g; Protein 26 g

Photograph by Antonis Achilleos